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TPS70933 safe at 3.3V input?

Stefan Krueger
Intellectual 670 points
Other Parts Discussed in Thread: TPS709Hello TI-Community,

i want to build a simple Breakout board for a 3.3V-Level Sensor Chip.
The Breakout should be 5V-Safe - so i need a LDO to regulated the 5V to 3.3V down.
For this i have choose the TPS70933 (its easy available for me).
if i use the board with a 3.3V host is it save to leave the TPS70933 in the circuit?
i mean can i just connect my 3.3V power-supply to the Input of the TPS and it would not be damaged?
i know it can't regulate at this point. but that is fine as the voltage is the required 3.3V.

Hope someone of you can give me a hint if this is a correct use-case.

sunny greetings
stefan
  • 0
    Intellectual 670 points
    i have found that this LDO has a Undervoltage Lockout (UVLO) (datasheet Chapter 7.3.3)
    but found no informaiton at what voltage level these shuts off.
    is it the 2.7V min input voltage?
    sunny greetings
    stefan
  • 0
    TI__Guru 50190 points

    HI Stefan,

    If you mean to have 3.3V out the output of the device, then absolutely the TPS709 can remain connected. The TPS709 is unique in that it has true reverse current protection meaning if at anytime, the VOUT is higher than VIN, the device will prevent current flowing in the reverse direction.


    As for UVLO, this question does come up and this UVLO on this IC is simply not well defined. As long and the IC is above or equal to 2.7V at VIN, it is guaranteed to work.

    I hope this answers your question.

  • 0 in reply to JCHK
    Intellectual 670 points
    Hi John,

    thanks for your information.with the reverse current protection that makes sens. fine :-)
    one more detailed: if i have the TPS70933 inline with the load at 3.3V input is this also fine?
    Like this: VIN --> TPS70933 --> Load
    with VIN = 3.3V
    will this also be safe? in the datasheet i have found 7.3.2 Dropout Voltage. it says:

    7.3.2 Dropout Voltage

    The TPS709 use a PMOS pass transistor to achieve low dropout voltage.
    When (VIN – VOUT) is less than the dropout voltage (VDO),
    the PMOS pass device is in the linear region of operation and the input-to-output resistance is the RDS(ON) of the PMOS pass element.
    VDO approximately scales with the output current because the PMOS device functions like a resistor in dropout.

    if i understand this correct it is fine - if i have minimal loads - i haven't found the RDS(on) specified in the datasheet.
    my feeling is that it will just work ;-) the load will see a minimal smaller Voltage - there will be a drop.. i will test it and report back.

    sunny greetings
    stefan
  • 0 in reply to Stefan Krueger
    TI__Guru 50190 points

    HI Stefan,

    Yes. with VIn at 3.3V the TPS709833 will do its best to try to regulate 3.3Vout. so it will basically be working as a load switch at this point. The actual output voltage will be VIN-VDO*ILOAD.

    Does this make sense?

    Regards,

  • 0 in reply to JCHK
    Intellectual 670 points
    Thanks for your Help! :-)
  • 0 in reply to Stefan Krueger
    TI__Guru 50190 points

    HI Stefan,

    Glad I could help! Please let me know if you have additional questions.

    Regards,